Monitoring Lakes from Space

Abhilasha Purwar
Sep 16, 2019 · 5 min read

On April 12, 2018, Cape Town in South Africa reached Day Zero” as labeled by local officials. After three consecutive years of anemic rainfall, April 12, 2018, become the day of the largest drought-induced municipal water failure in modern history.

On 19 June 2019, Chennai city officials declared that “Day Zero”, the four main city reservoirs stood at a meager 0.06%, offices closed, citizen waited hours in line for private tankers that sourced water from 100 miles outside the city. Trains and tankers ran from Tamil Nadu countryside to the city not with migrants but with molecules of life.

Water management is a two-sided phenomenon of surface and groundwater management. Surface sources also play a crucial part in the ground reservoir system by sourcing rainwater and refilling the ground system. However rampant destruction of surface water resources in past decades, including land encroachment, lake filling, garbage dumping has rendered many of this large rainwater collecting (hence groundwater replenishing) units useless and incapacitated.

Everywhere around us lakes are drying up, ponds becoming malls and offices, rivers becoming sewage streams, and freshwater volumes looking in the opposite supply direction of human consumption demand.

A report released by Niti Aayog paints a very grim picture of what is to come. According to the “Composite Water Management Index”, around 600 million people in India live in areas with high to extreme water stress and close to 70% of all water in India is contaminated to some degree. The report goes on to add that unless drastic measures are taken, by 2020, metropolitan cities like Delhi, Bangalore, and Hyderabad will face a water crisis that will affect around 10 crore people. By 2030, 40% of India’s population will be directly affected due to water shortage which will further derail economic and industrial activities in those regions.

According to government records, once upon a time during the British rule, there were 30,000 ponds in Madras Residency. The number today has drastically reduced, wherein only 3 major lakes Chembarambakkam Lake (3,645 Mcft), Red Hills Reservoir (3,300 Mcft) and Sathyamoorty Sagar (3,231 Mcft) have properly survived till today. In summer 2019, all of these lakes also ran dry.

What this really brings to light is the absolute need for proper and regular monitoring of lakes, include stronger predictive analysis to stall, solve, resolve, or at least foresee and prepare any such zero water days. Satellite imagery provides a highly efficient and scalable system to do so.

Blue Sky Analytics undertook a small project of monitoring a few lakes in Chennai between 2016 and 2019. Comparing the two summers, we find as high as 100% change in the surface area of these lakes.

This analysis is done using satellite imagery over major lakes of Chennai and image analysis techniques to calculate the water boundaries. In the images below, red denotes the extent of the lake three years ago taken as a reference and blue denotes the current extent.

The image on the left shows Red Hills Reservoir as on 5th June 2016, whereas the image on the right shows the same reservoir on 1st May 2017, where water surface levels have significantly dipped

Our results showing this change for Red Hills Reservoir, which is the same lake that has been the major hotspot among media after the water crisis struck Chennai. This is not the case with just one lake, but even the other major lakes of Chennai have shown drastic changes in their surface areas.

The image on the left is dated 6th May 2018. Within a year (6th June 2019), the surface level of the reservoir has almost completely vanished.

And not just the summers, winter months of 2018 have shown a similar trend. The decrease in lake area was quite noticeable, however, not 100%. Although, as can be seen, the water levels in the summer of 2018 were almost intact. This outlying behavior can be attributed to heavy rainfalls.

Red Hills Reservoir in October 2018

Similar results for other lakes of Chennai for the month of May 2019 can be seen below:

The image on the left shows Sathyamoorty Sagar lake on 31 May 2019, whereas the image on the right represents Chembarambakkam Lake on the same day

Considering the results, it becomes very obvious that the city and in the near future, the entire country is going to face a water deficit. It is time that we as citizens and our government considers climate change a matter of importance and takes appropriate measures. The government has to look for ways to harvest rainwater more efficiently so that it could be used in the next summers. As an obvious result of the water crisis, the Tamil Nadu government has reduced the water supply by 40%. However, this didn’t go well with the common people as they are finding other alternatives to get water.

Not knowing actually that they are bringing their own doom, people in many parts of India, including Chennai, have started installing submersible pumps in their localities. Imagine, every household drawing gallons of groundwater every day. Indeed, what Chennai saw today is not very far for the rest of the country. In some states, even the government has found installing submersible pumps as the only solution while they could have done rainwater harvesting instead, just to name a way of many. Ideally, stopping people from installing pumps and even penalizing them should be the main concern of the government.

Blue Sky Thinking

Using Technology & Data to save the Planet

Abhilasha Purwar

Written by

Founder & CEO, Blue Sky Analytics

Blue Sky Thinking

Using Technology & Data to save the Planet

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